Final answer:
The U.S. tried to manage slavery in western territories through legal means such as the Northwest Ordinance and political compromises, particularly the Compromise of 1850, but these efforts failed to quell the growing tensions between North and South, culminating in the Civil War.
Step-by-step explanation:
As the United States expanded westward, the contentious issue of slavery became increasingly difficult to manage. Initially, the Northwest Ordinance of 1787 offered a clear stance by prohibiting slavery in new territories north and west of the Ohio River. Many viewed this as an indication that slavery might eventually be phased out.
However, with the victory in the Mexican-American War and the ensuing Treaty of Guadalupe Hidalgo in 1848, the U.S. acquired vast new territories that reignited debates over slavery's expansion. Northerners and Southerners clashed over the issue. While Southerners wanted to extend slavery into new Western states such as California and New Mexico, Northerners, including abolitionists and free labor advocates, opposed this move. Ultimately, these disagreements were less about humanitarian concerns and more about political and economic implications.
The Compromise of 1850 was a major effort to address this by admitting California as a free state and enacting other measures to appease both sides. Despite these efforts, sectional tensions persisted, with events like the Fugitive Slave Act and the Kansas-Nebraska Act exacerbating divisions. The Dred Scott decision left an indelible mark on the national consciousness, further polarizing the nation. All these events cumulatively contributed to the Southern states' secession following Abraham Lincoln's election as president, ultimately leading to the Civil War.